Isopropyl alcohol (“IPA”; also known as isopropanol, 2-propanol, dimethylcarbinol, and sec-propyl alcohol) is an important commercial product. IPA finds use as a feedstock for other compounds, such as acetone, methyl isobutyl ketone, and isopropylamine, as a solvent in consumer products such as cosmetics and in industrial processes such as extractions, and also in medical uses such as disinfectants, antiseptics, liniments, and tinctures.
Large volumes of alcohols and ethers are produced annually by the catalytic hydration of olefins, particularly by the Indirect Hydration Process or Acid Catalyzed Hydration Process, where mono-olefins are hydrated in the presence of polybasic mineral acids. Chief among these processes is the “Sulfuric Acid Process”, in which the selected olefin feed is absorbed in a concentrated sulfuric acid stream to form an “extract” containing the corresponding alkyl ester of the sulfuric acid. Thereafter, water is admixed with the ester-containing extract to hydrolyze the ester and form the desired alcohol and ether, which are then recovered, generally by stripping with steam or some other heating fluid in an alcohol generator. See, for instance, Kirk-Othmer, Encyclopedia of Chemical Technology, 4th Ed., Vol. 20, pp. 216-236; U.S. Pat. Nos. 2,663,679; or 2,638,440.
The di-isopropyl ether (“DIPE”; often referred to as “isopropyl ether” or “IPE”) produced in these conventional processes is much less valuable than the IPA co-product. Accordingly, numerous proposals have been made to increase the IPA/DIPE ratio.
U.S. Pat. No. 2,105,508 relates to a process for producing DIPE by absorption of propylene. The extract liquid is passed from the absorption tower and introduced, after the addition of water or steam (to compensate for the water reacting to form the ether) to one of a series of ether generating pots, each equipped with steam coils. A vaporous product containing DIPE and IPA, is withdrawn, treated in a soda scrubber and passed to a distillation tower. Unreacted propylene is recovered as overheads in the distillation tower and can be recycled to the absorber. A sidestecam of condensed ether vapors is withdrawn from the top of the distillation tower, and an IPA-containing liquor is formed as bottoms product. The alcoholic bottoms is then, with or without removal of water, refluxed to the ether generating pots or passed to further refining as alcohol. Spent acid liquor remaining in the ether generating pots is recycled to the absorber. Reflux of the alcoholic bottoms to the ether generating pots is said to permit more accurate control of the ether generating conditions therein and to permit the acid to be concentrated to a higher strength before recycle to the absorber.
British Pat. No. 535,111 relates to a process for manufacture of ethers from olefins in which the sulfuric acid extract liquid is removed from the absorbing tower and is partially stripped in a stripping tower to form an ether-alcohol overhead mixture and a partially stripped extract as bottoms. The overhead mixture is passed to a separate tower for separation of the ether and to form an alcohol-containing bottoms. These alcohol-containing bottoms from the last tower are combined with the partially stripped extract, and sufficient water is added to make up that used in the formation of the ether. The resulting liquid stream is then recycled as the absorbate to the top of the absorbing tower.
U.S. Pat. No. 2,216,931 relates to aliphatic ethers including DIPE. According to the patent, such ethers are produced by a process in which the sulfuric acid extract containing olefin is split into two portions: a first portion is passed, after addition of water, to a stripping tower for formation of a vaporous overhead comprising the corresponding alcohol; and a second portion is fed directly to a reaction tower, together with the vaporous alcohol overhead formed in the stripping tower. In the reaction tower a liquid overhead stream is withdrawn and then passed to a generator for formation of vapors, which are then fed into a fractionating tower for recovery of the DIPE product as overhead and to form a bottoms product comprising IPA. This alcohol bottoms is then admixed with the stream containing the alcohol vapors withdrawn from the stripping tower for feed to the reaction tower.
In U.S. Pat. No. 2,533,808 the extract liquid is diluted with water and then passed to an alcohol generator for formation of dilute sulfuric acid as bottoms and to form overhead vapors comprising IPA and DIPE. This vapor product is then treated to separate the IPA as product and to recover the DIPE, which is recycled to the absorbing stage. In this process, the production of IPA can be increased by the recycle of the DIPE.
In U.S. Pat. No. 2,609,400 the propylene sulfuric acid extract liquid is stripped, without dilution with water, in a generator-stripper to form a mixture of ether and alcohol vapors. The partially stripped acid extract is then admixed with sufficient water (which can be added as steam via the steam injection into the stripper) to replace the water consumed in forming the alcohol and ether thus removed. Careful regulation of the extract temperature, steam temperature and pressure, and use of hot stripping gas is required to so control the heat balance of the generator-stripper to avoid dilution of the acid. Partially stripped acid extract is withdrawn from the generator-stripper and recycled to the olefin absorber, together with make-up acid as required. The ether/alcohol vapors withdrawn from the generator-stripper are scrubbed with a caustic solution to remove entrained acid, and the acid-free vapors are then condensed. The condensate, which comprises predominantly isopropyl alcohol, can be distilled to separate DIPE, which can be at least in part admixed with the partially stripped acid extract for recycle to the absorber.
In U.S. Pat. No. 2,994,721 the extract is passed into an ether generation zone from which vapors comprising predominantly DIPE are withdrawn as overhead. The remaining liquids are then diluted with water and fed to an alcohol generator for formation of overhead vapors comprising IPA and some DIPE. Dilute acid is withdrawn as bottoms product from the alcohol generator for concentration and subsequent recycle to the absorbing stage.
In German Offenlegungsschrift No. 2,759,237 propylene is absorbed in sulfuric acid to form an extract which is then treated to liberate the ether and alcohol. After separation of the alcohol, the ether is recycled to make more alcohol.
None of the foregoing processes are readily adaptable to vary appreciably the ratios of co-product isopropyl alcohol and di-isopropyl ether. In addition, most suffer in that recycling invariably results in recycling of impurities which have a negative effect on the process sooner or later.
A greater increase in the IPA/DIPE ratio is taught in U.S. Pat. No. 4,471,142. Propylene is contacted in an absorbing zone with aqueous sulfuric acid for formation of a liquid extract comprising sulfuric acid containing absorbed propylene values (i.e., all species in the mixture containing propyl or propylene moieties). The extract is contacted with a carefully controlled amount of water and the resulting hydrated extract is passed to an ether generating zone. Here, the hydrated extract is treated to liberate vapors containing DIPE and to form a liquid bottoms product comprising a depleted sulfuric acid extract containing absorbed propylene values and having a sulfuric acid concentration at least equal to the acid concentration in the extract liquid. The depleted extract is divided into two streams. The first stream is passed to an alcohol generator, after addition of water, to form an overhead product comprising predominantly isopropyl alcohol and a bottoms product comprising a dilute sulfuric acid stream. The second portion of said bottoms product is recycled to the absorbing zone. However, this method still produces DIPE in the amount of about 10% by weight.
Numerous patents are directed to the production of alcohols from ethers wholly separate from these olefin hydration processes. For instance, U.S. Pat. No. 1,602,846 relates to a process for converting methyl ether, obtained by the hydrolytic decomposition of methyl chloride, to methyl alcohol by reacting the former with steam over a refractory oxide in a tube. There is no distillation contemplated. Rather, methyl alcohol is recovered from the cooled reaction mixture by scrubbing with water. Furthermore, the patent explains that the process disclosed therein is “not applicable to all ethers”.
U.S. Pat. No. 2,115,874 teaches that the process taught in the aforementioned U.S. Pat. No. 1,602,846 is inoperative for the treatment of ethyl ether and higher ethers. This patent teaches an appropriate catalyst for vapor phase hydration of alpihatic ethers. The aliphatic ether is mixed with water vapor and the mixture of reactants is passed over a catalytic mass in a reaction zone at elevated temperatures. After leaving the reaction zone, the liquid condensate is fractionally distilled to separate the alcohol from the ether.
U.S. Pat. No. 3,634,534 teaches a process specifically envisioned to be used to separate linear olefins from tertiary olefins. A mixture is fed to a first distillation column reactor wherein tertiary olefins are reacted with an alcohol (such as methanol). Alcohol is removed from the lower part of the second distillation column reactor and recycled back to the first distillation column reactor.
U.S. Pat. No. 4,250,328 teaches separation of an ester from a reaction mixture comprising an ester, alcohol, organic acid, and water. The unreacted alcohol is removed as an ester-water azeotrope overhead.
Other processes include: U.S. Pat. No. 4,581,475, which teaches producing a lower aliphatic alcohol by splitting ethers over a catalyst in the presence of water; U.S. Pat. No. 5,043,486 teaching a method of producing alcohols from ethers without the use of catalysts; and yet another process is taught by U.S. Pat. No. 5,571,387, using an apparatus comprising a distillation zone and adsorption zone.
of the aforementioned patents teach a process involving utilizing a catalyst set within a distillation column, i.e., “catalytic distillation”. It has been suggested in the past to apply catalytic distillation to various processes, such as butene isomerization (U.S. Pat. No. 2,403,672); the hydrolysis of low molecular weight olefin oxides to produce mono-alkylene glycols (see U.S. Pat. No. 2,839,588); the production of methyl tertiary butyl ether (MTBE; see U.S. Pat. No. 3,634,535); and the production of tetrahydrofuran (see U.S. Pat. No. 4,079,068). In general the term “catalytic distillation” (or “reactive distillation”) covers any distillation or fractionation process or apparatus wherein the distillation column contains a catalyst for chemical conversion during separation.
Recognized advantages attributed to the catalytic distillation concept include a decrease in the capital cost of the plant needed to perform the process, the ability to achieve a higher degree of conversion, and the ability to perform processes which formerly were performed only in a batch type operation on a continuous basis.
The use of an aqueous acid contacting a substrate within a distillation column is taught in U.S. Pat. No. 2,045,785. In this process, steam and ether are introduced together at the bottom of a distillation column. An aqueous acid solution is introduced at the top of the distillation column. A “catalytic contact zone” is formed by the distillation column packing, and the alcohol is recovered in the acid liquor, which is then sent to a distillation column where the alcohol is removed overhead, along with unreacted ether. This mixture is then sent to another distillation column, where the alcohol and ether are separated. It is taught that “if the catalyst is allowed to continuously concentrate”, a large percentage of olefins results. The aspect of avoiding concentration of the catalyst is explicitly claimed. In a second embodiment, the reactor distillation column is at such a temperature that the alcohol and unreacted ether are taken overhead, and the acidic liquor is taken as bottoms.
U.S. Pat. No. 4,232,177 teaches a method using catalytic distillation wherein a mixed feed stream of isobutene and normal butene is fed into the lower end of a distillation column and methanol is fed into the upper end of the same column, the column being packed with a fixed bed catalyst. Methyl tertiary butyl ether (MTBE) is the product.
U.S. Pat. No. 4,447,668 teaches passing a feed stream comprising alkyl tertiary butyl ether (such as MTBE) over a fixed bed catalyst to produce an isoolefin and alcohol. There is no water (or steam) used in the catalytic distillation column. The alcohol is separated from the dissociation product stream as a bottom fraction, and the alcohol depleted product stream is then contacted with a second catalyst to form diisobutene.
U.S. Pat. Nos. 5,204,064 and 5,345,006 describe a method and apparatus for conducting catalytic distillation which allows for maintaining a liquid level in selected portions of the catalyst bed. In one embodiment, t-butyl alcohol is produced by the hydration of isobutylene Unreacted butylene, water, and inerts (e.g., other C4s) are taken overhead and TBA is recovered as bottoms.
U.S. Pat. No. 5,585,527 discloses a process for separating a first component from a second component of a process stream in a “single vessel” including a “membrane separation zone” and a distillation zone. The distillation zone may contain a “separation catalyst”. Specific applications envisioned include the separation of IPA and water in a process including forming DIPE from IPA. The patent also discloses the production of IPA from DIPE in an “IPA reactor that may be a stirred tank or fixed bed reactor. The effluent stream from this IPA reactor that is put through the “single vessel” reactor of the invention.
However, none of these address production of IPA by catalytic distillation and none teach anything about improving hydration of olefins processes. Thus, the aforementioned problems concerning the IPA/DIPE ratio still remain to be solved. Moreover, there still remains the need for an efficient means of producing IPA from DIPE.